Symmetrically triggerable bistable relay circuit



July l1, i967 B. l. KEPRTA, JR 3,330,997

SYMMETRICALLY TRIGGBRABLE BISTABLE RELAY CIRCUIT Filed Dec. 2, 1964 INVENTOR enough current from the relay United States Patent Ofitce 3,330,997 SYMMETRICALLY TRIGGERABLE BISTABLE RELAY CIRCUIT Buran I. Keprta, Jr., Norristown, Pa., assignor to Philco- Ford Corporation, a corporation of Delaware Filed Dec. 2, 1964, Ser. No. 415,370 9 Claims. (Cl. S17-148.5)

The present invention relates to relay circuitry, and more particularly to a symmetrically triggerable bistable relay circuit.

A bistable circuit is said to be symmetrically triggerable when successive identical pulses applied to a single input thereof will successively switch the circuit from one of its stable states to the other and back again. symmetrically triggerable bistable circuits have wide utility in computer and control circuitry. Such circuits have heretofore principally taken the form of cross-coupled inverting amplifiers (e.g., transistors or vacuum tubes) 'with a double diode steering gate -arranged to steer successive input pulses to different sides of the circuit so as to enable the symmetrical triggering mode of operation. Symmetrically triggerable bistable relay circuits have taken the form of an expensive and relatively high power consuming polar relay or one or more amplifying devices and a simple relay.

OBJECTS Accordingly several objects of the present invention are:

(1) to provide a new and improved symmetrically triggerable bistable circuit,

(2) to provide a new and improved bistable relay circuit which doe-s not require special relays or amplifier devices,

(3) to provide a symmetrically triggerable bistable relay circuit -of extreme simplicity, reliability, and low cost.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the ensuing description thereof.

SUMMARY In accordance with the present invention a symmetrically triggerable bistable relay circuit comprising a single-pole, double-throw relay whose field coil, in combination with a series resistor, is connected across a voltage source. When the armature of the relay is placed in the deenergized position, it will remain there because a current path is connected in series with the resistor and in shunt with the relay coil, thereby increasing the voltage drop across the resistance and dropping the voltage across the relay coil below the point at which the relay will pull in. When the armature of the relay is placed in the energized position, it will remain there because an impedance is connected in shunt with the resistor so that `enough current is drawn through the relay Held coil to hold the relay in position. The relay armature can be moved to the energized position by momentarily closing a switch which will allow a current surge to ow through the relay coil. When the armature is in the energized position, a m-omentarily closing of the same switch will divert coil to return the armature to the deenergized position.

DRAWING FIG. 1 of the drawing shows a bistable symmetrically triggerable relay circuit according to the present invention.

FIG. 2 shows a m-odified version of the circuit of FIG.

3,33%,997 Patented July 11, 1967 1 utilizing a transistor switch and adapted for operation with la burst triggering signal.

FIG. I Description The basic circuit of the present invention is shown in FIG. 1 of the drawing. The circuit includes a relay 10, power sources 12a and 12b (which may comprise separate power sources each having one terminal connected t-o the same reference point 13 as shown, or a single power source), resistors 14, 1'6, and 18, a capacitor 2t), and a single-pole, single-throw, momentary contact type switch 22. Relay 1o includes a field coil winding and an armature 15 which is switchable either to point A or point B to form part of a double-throw, single-pole switch. The armature 15 is shown in the nonenergized or rest position of the relay in which it makes electrical contact with point A. Armature 15 may be mechanically biased to this rest position in any convenient manner. When the field coil of the relay 10 is energized (i.e., when suliicient current flows therethrough), the armature will make electrical contact with point B, and will of course be returned to point A by the mechanical bias when the field coil is deenergized. The relay may have additional armatures and contacts for operating other control circuitry, as desired. One end of the field coil 10 of the relay is connected to source 12b and the other end is connected directly to the armature 15 and to reference point 13 via resistor 16. Point A is connected to source 12a va resistor 14, and point B is connected to reference point 13 via resistor 18 which is paralleled -by capacitor 20. Manually operated switch 22 is connected across points A-B so that these points will be connected together when switch 22 is closed.

As is well known, relays generally have two critical values of current a-ssociated with their field coil windings. The rst and higher value is the pull-in current which is the current required to operate the armature of the relay coil from the mechanically biased rest position to the energized position. The second and lower value of current is the hold current which is that value of current sutiicient to maintain the relay armature in the energized position. I'f the current through the field winding of a relay is reduced below the hold current value, the armature of the relay will return to its deenergized or rest position. Values for relay pull-in and hold currents will depend on relay design but typically may be 7 and 4 milliamperes, respectively.

The circuit of FIG. l is designed to operate so that when the armature 15 of relay 10 is in either position, a momentary closure of switch 22 will change the position of the relay armature to its other stable position. A second closure of switch 22 will return the relay armature to its intital position, and so forth.

Assume that the relay armature is in contact with terminal A as shown. The relay will remain in contact with terminal A because the resistance values of resistors 14 and 16 are selected so that the current flowing through resistor 14 will create a voltage drop across resistor 16 sufficient to maintain the current though field coil of relay 10 below the pull-in value required to operate the armature 15. If switch 22 is momentarily closed, contact will be made between points A and B. Since capacitor 20 is uncharged, a relatively large initial current surge will flow from source 12b through the field coil of relay 10, switch 22, and capacitor 20 to ground. This initial current surge will be greater than the pull-in current value of the relay 10, causing the relay to pull the armature 15 to point B. Current will be drawn from source 12b through the relay field coil in series with the parallel combination of resistors 16 and 18. The resistance values of resistors 116 Iand 18 Iare selected so that this current will be above Y 3 the hold current value of the relay, causing the armature to remain in Contact with point B.

If switch 22 is again closed, point A will be connected to pointV B and to the upper terminals of resistors 16 and 18. This will add the current through resistor 14 to the current already present in resistors 16 and 18. Thus the voltage across resistors 16 and 18 will increase, leaving insufficient voltage across the field coil of Vrelay to hold the same energized. Accordingly the armature of relay 10 will return to point A. Capacitor 20 will not interefere rwith this operation since it will be charged when the relay armature is in contact with point B.

It will be apparent that various other means may be used to connect point A and B in lieu of switch 22.

FIG. 2-D escription In the circuit of FIG. 2 of the present invention a PNP transistor 24 is used in lieu of switch 22. Also the circuit of the invention is shown adapted for operation with a burst triggering signal such as shown in waveform 26. In FIG. 2 parts having like counterparts in FIG. l have been identified with like reference numerals.

The circuit of FIG. 2 is identical to the circuit of FIG. 1 with the following exceptions. The emitter-collector path of transistor 24 is connected between points A and B,'With its collector connected to point A and its emitter connected to point B. The Ibase is connected to one side of t-he secondary winding of input transformer 28, the other sider of which is connected to the upper terminals of resistor 18 and conductor 20. The upper terminal of the parallel combination of resistor 20 and capacitor 18 is also connected to the emitter of transistor 24 =by a bias resistor 30. Transformer 28 is designed to receive an input signal burst such as is shown in waveform 26. A bypass capacitor 32 is connected from thejunction of resistors 18 and 30 to armature 15 so as to bypass the emitter to collector circuit of transistor 24 when armature makes contact with point A. A second set of relay contacts constituting a single pole, single throw switch is shown at 34. Contacts 34 are illustrative of additional contacts operated by relay 10 which may be designed to operate any external circuit as desired.

FIG. Z-Operaz'on The operation of the circuit of FIG. 2 is generally similar to that of FIG. l. Assume that armature 15 is in contact with point A. A signal burst such as 26 applied to the input winding of transformer 23 will render transistor 24 intermittently conductive. This will tend to cause intermittent current pulses to flow through the coil of relay 10, armature 15, transistor 24, resistor 30, and the low impedance presented by discharged capacitor 20. During the positive intervals of burst 26, when transistor 24 is nonconductive, capacitor 32 will bypass the emiter-collector circuit of transistor 24 and resistor 3tlg thereby effectively smoothing the current pulses through the coil of relay 10 connecting point A to point B. This will cause a continuous current surge through the field coil of relay 10 which will pull armature 15 to point B.

If a continuous negative input pulse is to be applied to the base of transistor 24, bypass capacitor 32 may be eliminated.

When armature 15 is in contact wit-h point B, a second burst identical to 26 will -once again cause transistor 24 to become conductive, connecting points A and B, and allowing current from source 12 to flow through resistor 14 and resistors 16 and 18 to decrease the current through the relay field coil below its hold value so that the armature will return to point A. If the armature is at point A and a long duration AC signal is applied in lieu of burst 26, the armature will be switched to point B and will then return to point A. If the armature is at point B when the long duration AC signal is applied, the armature will switch to point A and will not return to point B since capacitor will have been charged by the signal current. Thus the use of a long duration AC input signal provides a convenient way of setting several relays in the same position.

The circuit of FIG. 2 was used successfully in an ultrasonically triggered remote control operation. Burst 26 was generated by the tapping of a rod at a remote location to produce a 40 kc. supersonic signal. The supersonic 40 kc. signal from the rod was transformed to an electrical signal, amplified and applied across the input winding of transformer 28 to operate the circuit of the present invention.

In one operational embodiment of the circuit of FIG. 2, the following component values were used. Source 12 (equivalent to sources 12a and 12b) had a potential of l5 volts, resistor 14 was 680 ohms, resistor 16 was 2700 ohms, resistor 18 was 3900 ohms, and resistor 30 was 3.3 ohms. Capacitor 20 was 100 microfarads, and capacitor 32 was 5 microfarads. Relay 1f) had a pull-in current of 7 ma., a hold current of 4 ma., and a field coil resistance of 750 ohms.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be apparent that various modifications and other embodiments thereof will occur to those skilled in the art within the scope of the invention. Accordingly, it is desired that the scope of the invention be limited by the appended claims only.

I claim:

1. In combination: a relay having a field coil and an armature, said armature being connected to one terminal of said field coil, said armature being arranged to contact a first terminal when said relay is unenergized and a second terminal when said relay Vis energized, a first resistive impedance connected between the common terminal of said field coil and said armature and a reference potential point, the other terminal `of said field coil being connected to a voltage source, said first terminal being connected to a voltage source via a second resistive irnpedance, said second terminal being connected to a reference potential point via a third resistive impedance paralleled Iby a capacitor, and means for selectively connecting said first terminal to said second terminal.

2. The invention of claim 1 wherein said means comprises a switch. Y

3. The invention of claim 1 wherein said means comprises a transistor.

4. The invention of claim 3 wherein the collector of said transistor is connected to said first terminal, the emitter of said transistor is connected to said second terminal, said combination further comprising a bypass capacitor connected between said second terminal and said one terminal of said field coil.

5. A bistable circuit comprising, in combination:

(a) a relay includingV an armature and a field coil having first and second terminals, said armature arranged to (1) make contact with a third terminal when said field coil is not sufficiently energized to actuate said armature and (2) make contact with a fourth terminal when Vsaid field coil is sufficiently energized to actuate said armature, said armature being electrically connected to said second terminal of said field coil,

(b) a resistor connected between said second terminal and a point at reference potential,

(c) means connecting said first terminal of said field coil to a voltage source,

(d) a resistor connected between said third terminal and said voltage source,

(e) a resistor and a capacitor connected between said fourth terminal and said point at reference potential, and

(f) means for selectively connecting said third terminal to said fourth terminal.

6. The combination of claim 5 wherein said means comprises a single pole single throw switch.

7. The combination of claim 5 wherein said means comprises a transistor.

8. The invention of claim 7 wherein the collector of said transistor is connected to said third terminal, the emitter of said transistor is connected to said fourth terminal via a bias resistor, and a capacitor is connected between said fourth terminal and said second terminal, whereby said circuit is triggerable by a burst of alternating current.

9. The invention of claim 8 further including an input transformer having signal input and output windings, said output winding being connected to the Ibase of said transistor and to said fourth terminal.

6 References Cited UNITED STATES PATENTS 2,764,715 9/1956 Lorenz 317-151 2,788,473 4/ 1957 Breckman 317-151 3,003,088 10/1961 Hechler 317-151 3,159,773 12/1964 Elliot 317--151 X FOREIGN PATENTS 1,146,950 4/ 1963 Germany.

MILTON O. HIRSHFIELD, Primary Examiner. I. A. SILVERMAN, Assistant Examiner. 

1. IN COMBINATION: A RELAY HAVING A FIELD COIL AND AN ARMATURE, SAID ARMATURE BEING CONNECTED TO ONE TERMINAL OF SAID FIELD COIL, SAID ARMATURE BEING ARRANGED TO CONTACT A FIRST TERMINAL WHEN SAID RELAY IS UNENERGIZED AND A SECOND TERMINAL WHEN SAID RELAY IS ENERGIZED, A FIRST RESISTIVE IMPEDANCE CONNECTED BETWEEN THE COMMON TERMINAL OF SAID FIELD COIL AND SAID ARMATURE AND A REFERENCE POTENTIAL POINT, THE OTHER TERMINAL OF SAID FIELD COIL BEING CONNECTED TO A VOLTAGE SOURCE, SAID FIRST TERMINAL BEING CONNECTED TO A VOLTAGE SOURCE VIA A SECOND RESISTIVE IMPEDANCE, SAID SECOND TERMINAL BEING CONNECTED TO A REFERENCE POTENTIAL POINT VIA A THIRD RESISTIVE IMPEDANCE PARALLELED BY A CAPACITOR, AND MEANS FOR SELECTIVELY CONNECTING SAID FIRST TERMINAL TO SAID SECOND TERMINAL. 